In wrist trauma cases, injury commonly occurs to the ligaments stabilizing the scaphoid 10, a bone located near the thumb. (See FIG. 1.) When injury occurs, the ligaments are stretched or torn, thereby increasing the mobility of the scaphoid 10 with respect to the other carpal bones. Thus, injury to the ligaments can be detected by measuring the displacement of the scaphoid 10 in response to an applied force.
In recognition that injury to the ligaments can be detected in this manner, Watson developed a "scaphoid" test. See Watson, H. K., in Operative Hand Surgery, 2nd ed. Green, D. P., editor. Churchill Livingston, New York, 1988, p. 143. A clinician performs the scaphoid test by placing his four fingers on the back of the subject's radius and his thumb on the scaphoid 10. (See FIG. 2.) The right hand is used to examine the right wrist and vice versa. While moving the subject's hand from side to side, the clinician holds the scaphoid 10 in place with his thumb and applies a force to rotate the scaphoid 10 and drive the proximal pole of the scaphoid 10 dorsally. Excessive movement may indicate ligamentous injury. Once thoroughly familiar with the test, the clinician can readily detect excessive movement of the scaphoid 10.
The Watson "scaphoid" test, however, is extremely subjective and difficult to replicate. Because the test is performed strictly by sense of touch, results of the examination are inconsistent from one subject to the next and are highly operator dependent.